Understanding the issues:
Chemical Pollution
Chemical pollution is a pervasive but largely invisible driver of river degradation across the UK.
Modern society relies on thousands of synthetic chemicals used in industry, agriculture, medicine, and everyday consumer products. Many of these substances eventually find their way into our rivers through wastewater, agricultural runoff, industrial discharges, and urban drainage systems. Once in the environment, some chemicals persist for decades, accumulate in wildlife, and disrupt ecosystems. Addressing chemical pollution requires stronger regulation, improved wastewater treatment, and greater transparency about the chemicals entering our waterways.
Key facts
PFAS “Forever Chemicals” can persist in the environment for more than 1,000 years.
Source: European EA
Nearly one third of male fish in english rivers show signs of feminisation caused by chemical pollution
Source: Environment Agency
What is chemical pollution?
Freshwater chemical pollution is the presence of synthetic or industrially produced substances that are not naturally occurring, or that occur at concentrations above natural background levels. These chemicals can cause harm to ecosystems, wildlife, and human health.
Unlike sewage or algal blooms, chemical pollution is usually invisible and can come from many different sources. Some pollutants like Per- and polyfluoroalkyl substances (PFAS), better known as “forever chemicals”, persist for years and can build up in the environment; others like hormone disrupting chemicals can have an impact even at very low levels and these mixtures often go undetected. Yet it is one of the principal reasons that rivers in England are failing environmental standards.
Pictured: Testing for chemical contaminants
According to the Environment Agency’s River Basin Management Plans (2022) and the Water Framework Directive, not a single river in England achieves “good chemical status”. These chemical pollutants enter rivers through multiple pathways including:
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- Agricultural and road run-off
- Industrial discharges
- Household waste
- Spreading of sewage sludge on agricultural land
- Leaching from landfills and contaminated sites
Once released, many chemicals are extremely persistent and can remain in the environment for years or even decades. They accumulate in sediments, soils, and living organisms, and can continue to cycle through river systems long after their initial release.
A significant proportion of chemical pollution enters rivers through wastewater. However, conventional sewage treatment works were never designed to remove many modern synthetic chemicals like PFAS, pharmaceuticals or microplastics. Both the National Audit Office (2023) and the House of Commons Environmental Audit Committee have warned that current infrastructure is not equipped to deal with the variety and volume of chemicals in use today.
While some substances are regulated under Environmental Quality Standards (EQS), monitoring is limited. The Environment Agency tests for only a fraction of the tens of thousands of chemicals registered for use under UK REACH, the UK’s post-Brexit regulatory framework for chemicals.
What chemicals are polluting our waterways?
Modern rivers receive a complex mixture of chemicals originating from agriculture, industry, wastewater and consumer products, including:
The impacts
Chemical pollution has wide-ranging and often poorly understood impacts on freshwater ecosystems. It is increasingly recognised as a significant driver of biodiversity loss, affecting species behaviour, reproduction and survival across aquatic food webs. In response, governments around the world have committed to reducing chemical pollution as part of international biodiversity goals, including under the Kunming‑Montreal Global Biodiversity Framework, which aims to significantly reduce pollution risks and their impacts on biodiversity by 2030. However, existing regulatory frameworks struggle to keep pace with the rapid production and use of new synthetic chemicals, leaving many substances insufficiently monitored or controlled in freshwater environments.
Ecological disruption
One of the most significant impacts of chemical pollution is the disruption of biological systems and processes. Many of the chemicals that are polluting our rivers act as endocrine disrupting chemicals, which means they interfere with the cells that control growth, development and reproduction in aquatic species.
For example, long term studies by the Environment Agency of wild fish populations in English rivers have documented male fish developing female reproductive tissue following exposure to oestrogen and oestrogen-mimicking chemicals at around one third of sampled sites. These changes reduce fertility and contribute to the long-term decline in fish populations, with estimates from the Game and wildlife conservation trust showing some species have crashed by nearly 80% over the past decades.
Biodiversity loss
Chemical pollution can also reshape the structure of entire river ecosystems. Many aquatic insects such as mayflies, stoneflies and caddisflies are extremely sensitive to pesticides and other toxic substances entering rivers through agricultural runoff and wastewater.
Scientific studies have shown that chronic insecticide exposure significantly reduces aquatic invertebrate abundance and diversity, shifting rivers toward pollution-tolerant species. Because these insects form the base of freshwater food webs, their decline can cascade through the ecosystem, affecting fish, birds and mammals that rely on each other for food.
Bioaccumulation and contamination
Many chemical pollutants are persistent and bioaccumulative, meaning they build up in organisms and increase in concentration as they move up the food chain. Contaminants absorbed by algae and invertebrates are transferred to fish and then to predators such as birds and mammals. Substances including PFAS, mercury and industrial chemicals have been detected in fish, otters, and birds of prey across Europe, demonstrating how contamination of waterways spreads through entire ecosystems and can persist for decades.
Human health
Chemical pollution is also a risk to human health. Rivers contaminated with chemicals pose risks through recreational contact, consumption of contaminated fish, and abstraction for drinking water supplies. Certain widely detected chemicals, including PFAS, are associated with serious long-term health concerns, according to the European Environment Agency, including effects on the immune system, thyroid disease, reproductive and developmental outcomes, and increased risk of some cancers.
Chemical combinations
This sheer variety of different chemicals is a critical issue in itself. These substances can interact in ways that increase toxicity, meaning that combinations of chemicals may cause harm even when each individual substance present is below its regulatory safety threshold. This phenomenon, known as mixture toxicity, is increasingly recognised as one of the most significant challenges in understanding and regulating chemical pollution. Yet, regulatory compliance in the UK is still assessed substance-by-substance.
The Solutions
Chemical pollution is one of the most complex and poorly controlled pressures on our rivers, and current systems are not equipped to deal with it. Many of the substances now found in freshwater are not effectively regulated, monitored or removed, allowing them to build up in the environment over time.
Tackling this requires action across multiple fronts — reducing harmful chemicals at source, upgrading wastewater treatment, improving monitoring, and strengthening regulation to reflect how these substances behave in the real world.
The sections below set out some of the key interventions needed to address chemical pollution and reduce its impact on rivers:
Control pollution at source
The most effective intervention is prevention at source. This means restricting or phasing out non-essential uses of hazardous substances, particularly PFAS and other chemicals that do not readily break down in the environment.
The principle is increasingly recognised in environmental policy as “control at source”. It focuses on reducing the production and use of harmful chemicals before they reach wastewater systems and waterways, rather than relying on costly downstream treatment once contamination has already occurred.
Strengthening the UK’s chemicals regime, UK REACH, and the Government’s new PFAS plan, will be essential to ensure that hazardous substances are properly assessed and regulated before they accumulate in the environment.
Upgrade wastewater treatment
Current sewage treatment works are not designed to remove many contaminants such as pharmaceuticals, PFAS and microplastics. Conventional treatment processes primarily target nutrients and organic waste, meaning many synthetic chemicals pass through treatment plants and enter rivers.
Reducing these emissions will require investment in advanced treatment technologies, such as activated carbon filtration, ozonation and membrane systems, which are capable of removing a wider range of micropollutants from wastewater.
Countries such as Switzerland have already introduced national requirements for wastewater treatment plants to install additional treatment stages to remove chemical pollutants.
Expand monitoring and transparency
Monitoring requirements must also expand beyond a narrow list of priority substances so that regulators and the public have an accurate picture of chemical pressures in catchments. This includes testing for a wider range of contaminants, improving the spatial coverage of monitoring networks, and making environmental data more accessible so that communities, researchers and regulators can better identify pollution sources and trends.
Reform land management practices
Agriculture is a major pathway through which pesticides, heavy metals, PFAS and other chemicals enter rivers. Improving land management practices can significantly reduce these losses.
A key issue is the spreading of sewage sludge on agricultural land. Sludge can contain a wide range of contaminants, including PFAS, heavy metals and other persistent chemicals, which can accumulate in soils and be washed into rivers over time. Despite this, current regulation and monitoring are limited, and the practice continues at scale. Strengthening controls on sludge spreading — including better testing, tighter limits and greater transparency — is essential to reduce this pathway of pollution.
Alongside this, measures such as integrated pest management, reduced pesticide inputs, buffer strips along rivers and more careful nutrient management can help limit pollution, particularly during rainfall events.
Regulation
Finally, regulatory approaches must evolve to reflect scientific understanding. Chemicals do not occur in isolation; they interact in complex mixtures that can amplify toxicity. Yet compliance in England is still largely assessed substance-by-substance. Updating regulatory frameworks to account for cumulative and mixture effects is critical if environmental standards are to protect ecosystems effectively from the start.
